This invention relates generally to an air generation unit (AGU) suitable for an aircraft. In particular, the invention relates to the operating lifetime of a heat exchanger in an AGU.
AGUs typically include at least one air cycle machine (ACM) and at least one heat exchanger that receives air from a pressurized air source, such as bleed air from an engine, to provide cooled air to the aircraft cabin and cockpit.
An AGU may include a heat exchanger having primary and secondary heat exchangers. Bleed air is taken from an intermediate or high pressure stage of the turbine engine. The bleed air is precooled within the primary heat exchanger with the heat being rejected to ram air and then communicated to the compressor of the ACM. After compression, the air is communicated through a secondary heat exchanger to a condenser. Condenser water vapor is extracted by a water collector, and the dehumidified air is sent to a turbine where the air is expanded to generate cold air. In larger aircraft, the AGU may include first and second turbines. The second turbine receives cold air from the first turbine and further expands the cold air to produce subfreezing air sufficient to cool larger aircraft. The cold air is sent to an environmental control system (ECS) that further conditions and distributes the air to the aircraft.
The primary heat exchanger is a component of an AGU that is susceptible to damage as a result of exposure to thermal cycling. Improvements of the primary heat exchanger will result in extended periods of service.